It is important to note in this context that the results of Booth
and Creighton were originally intended to show that quasilocal methods
lead to the same consistent results as pseudotensorial methods (which,
surprisingly, all lead to the very same expression, regardless of
the choice of the energy-momentum complex and gauge conditions [1]}, [2]}).
In fact, the compatibility is not very surprising from today's viewpoint
in that it has been shown by Chang, Chen and Nester [3]}
that any energy-momentum pseudotensor leads to an associated Hamiltonian
boundary term, so that it becomes clear that - within the quasilocal
Hamiltonian framework - pseudotensors either give rise to distinct
Dirichlet type boundary conditions or to Neumann type boundary conditions;
all of which are algebraic in terms of the metric. Consequently, however,
since the tidal heating results obtained in the literature appear
to be independent of the choice of boundary conditions, it is hardly
surprising that the purely quasilocal calculation of Booth and Creighton
leads to very similar results as those of earlier works on the subject
that used the pseudotensorial approach. This is not least the case
because, in the approximate calculations mentioned, the precise form
of the boundary conditions is not essential, because the results obtained
by using different boundary conditions deviate from each other only
in higher order.
